What would the easiest way to make an enemy follow you only if they see you?

[Baller20]

I would like to have an enemy move towards you only if you are in their line of sight. Like if I was behind a wall, they wouldn't follow me but if I turned the corner they would start following me. I'm a noob and I don't know how to make this happen. Can someone help me or at least explain how I would work this out? The game I'm making is a top-down style game.

 

[TheForeman847]

Check out collision_line(). You can use it to check for an object between two points. For example, check for a wall object between the player and the enemy.

 

[ObserverOfSin]

Step event:

image_angle = direction
  
if (!collision_line(x,y,player_obj.x,player_obj.y,obj_wall,0,0)) //// checks if there is no collision of obj_wall from x,y, to player_obj x,y
{
dir = point_direction(x,y,player_obj.x,player_obj.y)                /// sets variable dir as direction from x,y to player x,y
if    (dir>direction-fov and dir<direction+fov)                  /// checks if player is within a field of view of 'fov'  
     xor
      (dir+360>direction-fov and dir+360<direction+fov)
     xor
      (dir-360>direction-fov and dir-360<direction+fov)

   {
   move_towards_point(player_obj.x,player_obj.y,1)                       /// moves towards player_obj at a speed of 1
   } 
}
else
{
speed = 0   //// go back to patrolling or whatever
}

You'd need to set 'fov' and 'dir'

 

[Nocturne]

if    (dir>direction-fov and dir<direction+fov)                  /// checks if player is within a field of view of 'fov' 
     xor
      (dir+360>direction-fov and dir+360<direction+fov)
     xor
      (dir-360>direction-fov and dir-360<direction+fov)

This can be condensed down to:

if abs(angle_difference(dir, direction)) < fov // Angle_difference arguments might need reversed... I always get them in the wrong order... :P
{
// Do something
}

 

[rytan451]

if abs(angle_difference(dir, direction)) < fov // Angle_difference arguments might need reversed... I always get them in the wrong order... :P
{
// Do something
}

Since the angle_difference is inside abs, the order of the arguments isn't important. abs(a - b) = abs(b - a) after all. Also, the way that I remember the argument order for angle_difference is that a + angle_difference(b, a) is equivalent to a mod 360.

 

[Baller20]

Sweet! Thanks for all the help.